Posted
by
Soulskill
on Friday May 02, 2014 @11:13AM
from the E.T.-=-mc^2 dept.

KentuckyFC writes: "One of the main goals of the space program is to spot an Earth-like planet orbiting another star. And by Earth-like, astronomers mean a planet with liquid water, gaseous oxygen and even chlorophyll, or a light-harvesting molecule like it. The biosignatures of these molecules were all observed during the first Earth fly-by in 1990 when the Galileo spacecraft measured the light reflected off Earth as it flew past on its way to Jupiter. But if these biosignatures exist on more distant exoplanets, could we spot them today? Now astronomers have calculated how good the next generation of space telescopes will have to be to pick up these biosignatures of life. They say that gaseous water should be relatively straightforward to pick out and that oxygen will be more challenging. But the spectral signature of chlorophyll-like molecules will be much harder to spot, requiring significantly more sensitivity than is possible today (either that or a great deal of luck). That suggests a plan, they say. The next generation of space telescopes should look for water and oxygen on exoplanets orbiting nearby stars and only then begin the time-consuming and expensive task of looking for chlorophyll on the most promising targets. One spacecraft that might do this is the Advanced Technology Large-Aperture Space Telescope or ATLAST that is currently scheduled for launch in the 2025-2035 time frame."

If a planet has life on it. If we visit it, how much damage will that cause. I mean just the bacteria on our skin that is normally helpful, my thrive and kill off all the life on the planet that may not have such defenses.

That assumes the wayward bugs can metabolise anything on an alien world. Things like basic sugars, which I would assume are simple enough to be common, probably. But infecting a totally alien organism? Probably not.

Take staph. aureus for example. It can survive on humans of course, and a few domestic animals (maybe due to their long association with people) but apart from those I understand that it isn't common in other species. A bacteria that can easily cross species lines is one thing, but making the jump to an alien biology is quite another. Then again the biology might not be so alien if they're looking for worlds where the native plant life just happened to evolve chlorophyll.

That's while the nylon was surrounded by a world rife with food for the bacteria and countless varieties of pathogens. Evolution works on chance and brute force. The chance that any given mutation can happen is exceedingly low, but given the countless numbers of bacteria a nylon eating bacteria becomes an almost inevitability. What are the chances that a bacteria that can live on humans will survive long enough on an alien world to find a material is can metabolize? I think it really depends on just how sim

These are the kinds of questions that absolutely fascinate me about exobiology. If we discover life on another world (maybe even in our solar system) and it turns out to be completely different from life as we know it, that would be amazing, to study a completely different biology. If we find this life and is just like us, that would be equally amazing, because it would hint at common origins or common processes to the formation of life everywhere. Even if we find no other life, that's amazing, because it s

Come on, don't be negative: a new inhabitable world is much like an inhabitable new continent, and we already showed how our civilization is able to preserve the ecosystem we invade. Just ask the real Americans.

Even if we're biologically similar enough there's no huge need to send down anything but highly sterilised drones. Plus, you can learn an enormous amount just from low orbit observation, especially if you're sufficiently advanced to get there in the first place.

If a planet has life on it. If we visit it, how much damage will that cause. I mean just the bacteria on our skin that is normally helpful, my thrive and kill off all the life on the planet that may not have such defenses.

It doesn't matter because the reality is we couldn't get there, anyway.

Isn't chlorophyll tuned to the easiest bands of energy that come from our sun and don't get scattered by our atmosphere? Wouldn't a slightly different stellar color or atmospheric makeup dramatically change how stellar energy would be chemically captured?

It's not so much a big assumption as it is a starting point. There is probably a biosphere somewhere in the Universe that uses a red or yellow pigment for photosynthesis. The problem is that detecting it at a distance is much harder, because while we might see the spectral signature we couldn't be sure that it's life.

Looking for a biosphere that is very similar to that of Earth makes it much more likely that we'll be able to detect that it is in fact "life" and not something else. While we may miss 99% of the life in the Universe with this approach, if/when we do detect it, our confidence will be much higher.

Hence the line about "light gathering chemicals like it". There's a few different chemicals [berkeley.edu] that can be used by organisms in photosynthesis. Chlorophyll is simply the most popular on the surface of the Earth. Other pigments are optimum for regions that receive different light spectra than the surface. On worlds whose stars had different spectral maxima than Sol these pigments would likely be more abundant in photosynthetic life.

ISTR that chlorophyll is essentially a "voltage doubler", basically for red light. (Leaves are green because they use the red, and discard/reflect the green.) If you consider red to be between 600nM and 700nM, then a little more UV than we get might deliver enough content between 300nM and 350nM to be used directly for photosynthesis. I wonder how much UV would be needed to bypass the doubler, and if that would be too much for life, in general. Of course that would mean a hotter sun than ours, and I've more recently heard more about searching around red dwarves, where the leaves would more likely look black.

ISTR that chlorophyll is essentially a "voltage doubler", basically for red light. (Leaves are green because they use the red, and discard/reflect the green.) If you consider red to be between 600nM and 700nM, then a little more UV than we get might deliver enough content between 300nM and 350nM to be used directly for photosynthesis. I wonder how much UV would be needed to bypass the doubler, and if that would be too much for life, in general. Of course that would mean a hotter sun than ours, and I've more recently heard more about searching around red dwarves, where the leaves would more likely look black.

I asked a biology professor why leaves aren't black. I mean, it stands to reason that absorbing more of the spectrum would improve efficiency, right? He said leaves are green because green wavelengths would damage chlorophyll. I haven't further corroborated this, but it was interesting to consider.

It really doesn't matter. It's like that unbelievably sexy girl at the beach: you can look all you want, but since you'll never have her, why do that to yourself? With this, even if we find, water, oxygen, chlorophyll, and the unmistakable chemical signature of entire oceans filled with beer, it's irrelevant and a waste of time and money since we'll never be able to go there. Let's use this money to help undo the damage we're doing to the one little blue marble we *do* have access to and are cooking out

The intro is misleading. ATLAST has not a single dollar pledged to it. It has no "scheduled" launch date. It does have a lot of people thinking about it (and a very similar project, HDHST), but for now it exists purely in dreams and on paper.

Absolutely right: I was going to point out the same thing. It's many, many years away from any possible launch...

For reference, the James Webb Space Telescope (or NGST as it was then) was beginning to be picked up as a serious prospect by NASA, ESA, and the Canadian Space Agency in the late 1990's. It's due for launch now in 2018.

(This is not meant as a criticism: I've been closely involved with JWST since 1998 and know how hard it has been in terms of technology, programmatics, and politics to get

Every time I read something like this, I wonder if any habitable planets we find will still be habitable by the time we can get to them. If we find a habitable planet just a relatively close 10 light years away, then we're already seeing it as it was 10 years ago. Something could've changed there by the time we're seeing it. It's probably unlikely there'd be THAT much change in just 10 years, but then you have to figure it'd take us thousands of years to reach it with our current technology 'cause we can't [scientificamerican.com]